1. Field of the Invention
This invention relates to a solid state laser such as a laser diode-pumped solid state laser, and more particularly to a solid state laser in which fluctuation in the oscillation wavelength and/or the output power due to change in the length of the resonator is prevented.
2. Description of the Related Art
As disclosed, for instance, in Japanese Unexamined Patent Publication No. 62(1987)-189783, there has been known a solid state laser in which a solid state laser medium doped with a rare earth metal such as neodymium is pumped by a laser beam emitted from a semiconductor laser or the like.
In such a laser diode-pumped solid state laser, the oscillation wavelength is shifted toward the longer wavelength side as the environmental temperature becomes higher and toward the shorter wavelength side as the environmental temperature becomes lower, which changes the optimal drive condition of the laser, e.g., the temperature to which the temperature of the resonator is to be controlled, and causes fluctuation in the output power of the laser.
In order to overcome this problem, the applicant has proposed to contain the solid state laser crystal, the resonator and the like in an enclosed casing which is filled with gas the refractive index of which is closer to 1 than air or which is evacuated to lower than the atmospheric pressure. See Japanese Unexamined Patent Publication No. 9(1997)-266337.
Though these approaches can overcome the problem described above, the former is disadvantageous in that the manufacturing cost is increased and the latter is disadvantageous in that the properties of the solid state laser vary as the state of parts about the resonator varies from the time the casing is sealed to the time the solid state laser is assembled and adjusted.